Superflares on solar-type stars from the first year observation of TESS

TL;DR

This study analyzes superflares on solar-type stars using TESS data, revealing higher flare frequencies than Kepler, a power-law energy distribution, and insights into stellar magnetic activity and flare characteristics.

Contribution

First comprehensive analysis of superflares on solar-type stars using TESS data, including frequency distribution and energy-duration relationships.

Findings

Higher superflare frequency distribution than Kepler.

Power-law index of superflare energies is 2.16±0.10.

Energy-duration relation index is 0.42±0.01.

Abstract

Superflares, as strong explosions on stars, have been well studied with the progress of space time-domain astronomy. In this work, we present the study of superflares on solar-type stars using Transiting Exoplanet Survey Satellite ({\em{TESS}}) data. 13 sectors of observations during the first year of the {\em TESS} mission have covered the southern hemisphere of the sky, containing 25,734 solar-type stars. We verified 1,216 superflares on 400 solar-type stars through automatic search and visual inspection with 2-minute cadence data. Our result suggests a higher superflare frequency distribution than the result from {\em Kepler}. The reason may be that the majority of {\em TESS} solar-type stars in our dataset are rapidly rotating stars. The power-law index $\gamma$ of the superflare frequency distribution ($dN/dE\propto E^{-\gamma}$) is constrained to be $\gamma = 2.16\pm 0.10$, which is a little larger than that of solar flares but consistent with the results from {\em Kepler}. Because only 7 superflares of Sun-like stars are detected, we may not give a robust superflare occurrence frequency. And four stars are accompanied by unconfirmed hot planet candidates. Therefore, superflares are possibly caused by stellar magnetic activities instead of planet-star interactions. We also find an extraordinary star TIC43472154, which exhibits about 200 superflares per year. In addition, the correlation between energy and duration of superflares ($T_{\text {duration }} \propto E^{\beta}$) is analyzed. We derive the power-law index to be $\beta=0.42\pm0.01$, which is a little larger than $\beta=1/3$ from the prediction according to magnetic reconnection theory.